The present invention relates to a polyacetal ABA type block copolymer having a shorter crystallization time, a higher roundness and distinguished long-term dimensional characteristics and durability, when molded. In addition, such block copolymer has superior compatibility with other polymer compounds and superior adhesibility to inorganic fillers. Furthermore, the present invention relates to a composition comprising such a polyacetal ABA type block copolymer, and moldings obtained from the polyacetal ABA type block copolymer or a composition comprising the polyacetal ABA type block copolmer.
A polyacetal resin is a material with a distinguished slidability and is used preferably as gear material. However, in reality, the conventional polyacetal resins obtained by homopolymerization of formaldehyde or copolymerization of formaldehyde, trioxane and cyclic ether often fail to produce gears of large diameters, e.g. pitch circle diameters of 60 mm or larger, which are satisfactory from the viewpoint of performances, by injection molding. That is, (1) The larger the gear diameter, the thicker the gear itself, and the cooling time is prolonged in the injection molding step. As a result, such a problem has been encountered that the injection molding cycle will be prolonged in case of other resin materials than those having a higher crystallization rate and thus the productivity will be lowered. (2) In case of the conventional polyacetal resin, the roundness of large-diameter gears produced by injection molding is not satisfactory and as a result such a problem has been encountered that in copiers or printers using such gears, power transmission accuracy will be lowered, resulting in uneven dot distances and failure of clear print/image. (3) When large-diameter gears are injection molded from the conventional polyacetal resin, the dimensions of injection molded large-diameter gears are unstable when left standing for a long time, and application of such gears to copier or printers will give rise to failure in meshing between gears at pitch points, when used for a long time (in worst cases the meshing between gears will be brought into complete failure), causing generation of uneven vibration during the revolutionary transmission and generation of dislocated print/image. (4) Furthermore, the larger the gear diameter, the more unsatisfactory the gear durability, one of resin material properties, and thus application of such gears to copiers or printers gives rise to breakage of a gear tooth (gear teeth) due to wear, rupture or fatigue of gear when used for a long time, and thus the long-term functioning of copiers or printer cannot be so far guaranteed.
Attempts have been made with polyacetal block polymers to improve the problem of the conventional polyacetal resins, as proposed, for example, in JP-A-3-21657 and JP-A-5-9363, which disclose polyacetal polymers, which are AB type block copolymers, blocked at one end by alkylene oxide as an adduct to alcohol or carboxylic acid.
JP-A-4-306215 discloses AB type and ABA type polyacetal block copolymers comprising a polyoxymethylene segment (A) and a polymethylene segment (B), obtained by polymerizing one end or both ends of the polymethylene segment with formaldehyde, trioxane or the like in the presence of a compound containing one functional group selected from the group consisting of a hydroxyl group, a carboxyl group, an amino group, an ester group and an alkoxy group. It is further disclosed that hydrogenated polybutadiene can be used as a polymethylene segment.
Furthermore, JP-A-11-51154 discloses gears made from polyacetal copolymer having a specific monomer formulation, or the polyacetal copolymer admixed with xcex1-olefin oligomer, an inorganic filler or the like as resin materials.
However, the polyacetal copolymers disclosed in the foregoing references fail to obtain the above-mentioned characteristics necessary for the large-diameter gears.
An object of the present invention is to solve the foregoing problems and provide a polyacetal ABA type block copolymer and a resin composition comprising the block copolymer, which have a high crystallization rate and are capable of molding large-diameter gears with a high roundness and distinguished dimensional stability and durability.
As a result of extensive studies to solve the foregoing problems, the present inventors have found that a polyacetal ABA type block copolymer comprising a polyacetal copolymer and a specific polymer or a polyacetal resin composition comprising the ABA type block copolymer and a specific polymer compound are distinguished in the necessary characteristics required for large-diameter gears, that is, crystallization rate, roundness, dimensional stability and durability, and have established the present invention.
That is, the present invention provides:
[1] An ABA type block copolymer, which comprises polyacetal segments (A) and a hydrogenated polybutadiene segment (B) hydroxyalkylated at both ends, represented by the following formula (1): 
[where A comprises 95-99.9 mol % of oxymethylene units and 0.1-5 mol % of oxyalkylene units represented by the following formula (2): 
(where R2 is independently selected from the group consisting of hydrogen, an alkyl group, a substituted alkyl group, an aryl group and a substituted aryl group, and j is an integer selected from 2 to 6), and the terminal groups are polyacetal copolymer residues having a structure represented by the following formula (3): 
(where R2 and j have the same meanings as defined above), Bxe2x80x2 is a hydrogenated polybutadiene having an iodine value of 20 g-I2/100 g or less and containing 70-98 mol % of 1,2-bonds and 2-30 mol % of 1,4-bonds, R1 is independently selected from the group consisting of hydrogen, an alkyl group, a substituted alkyl group, an aryl group and a substituted aryl group, and k is an integer selected from 2 to 6 where two ks may be the same or different from each other], the hydrogenated polybutadiene segment (B) hydroxyalkylated at both ends having a number average molecular weight of 500-10,000 and the ABA type block copolymer having a number average molecular weight of 10,000-500,000;
[2] An ABA block copolymer as described in the foregoing [1], wherein Bxe2x80x2 is a hydrogenated polybutadiene containing 80-95 mol % of 1,2-bonds and 5-20 mol % of 1,4-bonds;
[3] A polyacetal resin composition, which comprises 100 parts by weight of a polymer compound (I) comprising 20-100% by weight of the ABA type block copolymer as described in [1] or [2] and 0-80% by weight of a polyacetal copolymer having a number average molecular weight of 10,000-500,000, represented by the following formula (4): 
(where R3 and R4 are independently selected from the group consisting of hydrogen, an alkyl group, a substituted alkyl group, an aryl group and a substituted aryl group, p=95-99.9 mol %, q=0.1-5 mol %, p+q=100 mol %, and z is an integer selected from 2 to 6), and 0.1 to 200 parts by weight of at least one of polymer compounds (II) having a number average molecular weight of 500 or more, selected from the group consisting of a polyolefin-based polymer compound, a polyurethane-based polymer compound, a polyester-based polymer compound, a polystyrene-based polymer compound, a polyacryl-based polymer compound and a polyamide-based polymer compound;
[4] A polyacetal resin composition as described in the foregoing [3], wherein the polymer compound (II) is a polyolefin-based polymer compound comprising xcex1-olefin-based polymer compound;
[5] A polyacetal resin composition, as described in the foregoing [4], wherein the xcex1-olefin-based polymer compound comprises 0.1 to 6 parts by weight of an ethylene-xcex1-olefin random copolymer having a number average molecular weight of 500-10,000, comprising 10-70 mol % of ethylene unit and 30-90 mol % of xcex1-olefin unit;
[6] A polyacetal resin composition as described in the foregoing [4], wherein the xcex1-olefin-based polymer compound is an xcex1-olefin-based copolymer modified by an unsaturated carboxylic acid or its acid anhydride;
[7] A polyacetal resin composition as described in the foregoing [3], wherein the polymer compound (II) is a polystyrene-based polymer compound comprising a copolymer of an aromatic vinyl monomer and a copolymerizable unsaturated monomer that can be copolymerized with the aromatic vinyl monomer;
[8] A polyacetal resin composition as described in the foregoing [3], wherein the polymer compound (II) is a polystyrene-based polymer compound comprising a block (a) comprising a styrene monomer and a block (b) comprising isoprene or isoprene-butadiene and containing 20 mol % or more of vinyl bonds;
[9] A polyacetal resin composition, which comprises 100 parts by weight of a polymer compound (I) and 0.1 to 100 parts by weight of an inorganic filler;
[10] A polyacetal resin composition, which comprises 100 parts by weight of polymer compound (I), 1 to 20 parts by weight of polymer compound (II) and 0.1 to 100 parts by weight of an inorganic filler;
[11] A polyacetal resin composition, which comprises a polyacetal resin composition as described in any one of the foregoing [3] to [10], and 0.01 to 0.2 parts by weight of at least two of difatty acid calciums (calcium salt of fatty acid) having 12-22 carbon atoms and/or 0.01 to 0.9 parts by weight of at least two of esters of a fatty acid having 12-22 carbon atoms with ethylene glycol;
[12] A molding comprising an ABA type block copolymer as described in the foregoing [1] or [2], or a resin composition as described in any one of the foregoing [3] to [11];
[13] A molding as described in the foregoing [12], wherein the molding is a large-diameter gear having a pitch circle diameter of 60 mm or more; and
[14] A molding as described in the foregoing [12], wherein the molding is a large-diameter gear having a pitch circle diameter of 100 mm or more.
ABA Type Block Copolymer
First, description will be made below of a novel ABA type block copolymer comprising polyacetal segments (A) (which may be hereinafter referred to xe2x80x9cSegment Axe2x80x9d) and a hydrogenated polybutadiene segment (B) hydroalkylated at both ends (which may be hereinafter referred to as xe2x80x9cSegment Bxe2x80x9d).
Segment B
Segment B in the present ABA type block copolymer is a hydrogenated polybutadiene hydroxyalkylated at both ends, represented by the following formula (5): 
(where Bxe2x80x2 and k have the same meanings as defined before).
Segment B can be prepared according to a process comprising subjecting butadiene (above 5% or less of other vinyl monomer or conjugated diene can be used together, if necessary, from the viewpoint of productivity, etc.) to anionic polymerization in the presence of an alkali metal such as sodium, lithium, etc. or a complex of an alkali metal with an aromatic compound as a catalyst to prepare a polybutadiene; and then adding alkylene oxide to both ends of the resulting polybutadiene; followed by treatment with a protonic acid such as hydrochloric acid, sulfuric acid, acetic acid, etc. to make a prepolymer; and by hydrogenation of the prepolymer.
The butadiene polymerization process is not particularly limited, but the hydroxyalkyl groups present at both ends of Segment B play an important role in the present ABA type block copolymer, and thus it is necessary to use a polymerization process capable of adding the hydroxyalkyl groups to both ends of polybutadiene.
Preferable process for making the prepolymer includes, for example, a process comprising reacting butadiene with a Lewis base type compound and an alkali metal in advance, thereby synthesizing a dimer dianion (see JP-B-40-7051), then reacting alkylene oxide or substituted alkylene oxide with living anions present at both ends of the dimer dianion, followed by treatment with protonic acid such as hydrochloric acid, etc.
The hydroxyalkyl residues (groups) present at both ends of the prepolymer typically include hydroxyethyl residues, hydroxypropyl residues, hydroxybutyl residues, hydroxypentyl residues, hydroxyhexyl residues, and their substituted alkyl or aryl residues; among which hydroxyethyl residues are preferable.
Description will be made below of a process for hydrogenating the prepolymer. So far well-known hydrogenation processes can be used, and nickel, cobalt, ruthenium, rhodium, palladium, platinum, etc. can be used as a hydrogenation catalyst. Preferable hydrogenation process includes, for example, a hydrogenation process using alcohol and an aliphatic hydrocarbon as a reaction solvent (see JP-A-7-247302).
For the present hydrogenated polybutadiene, it is preferable that a hydrogenation rate is 100% (i.e. structure without any unsaturated bond), but so far as the iodine value is not more than 20 g-I2/100 g (according to JIS K0070), the presence of unsaturated bonds in the polymer is no problem.
In the present invention, it is necessary to hydrogenate polybutadiene containing 70-98 mol % of 1,2-bonds and 2-30 mol % of 1,4-bonds, as set forth in the foregoing formula (1). The 1,2-bond content and 1,4-bond content of polybutadiene can be identified by 1H-NMR. The 1,2-bond content of more than 98 mol % or less than 70 mol % cannot satisfy the characteristics required for materials for large-diameter gears in the present invention. From the viewpoint of attaining more distinguished characteristics required for materials for large-diameter gears, it is preferable to use polybutadiene containing 80-95 mol % of 1,2-bonds and 5-20 mol % of 1,4-bonds. In the present invention, it is preferable to use polybutadiene with randomly distributed 1,2-bonds and 1,4-bonds.
Furthermore, it is desirable from the viewpoint of satisfying required for materials for large-diameter gears that Segment B has a number average molecular weight of 500-10,000 (in terms of polystyrene). From the viewpoint of attaining further distinguished characteristics required for materials for large-diameter gears, more preferable number average molecular weight of Segment B is 2,000-5,000 (in terms of polystyrene). Molecular weight distribution (Mw/Mn) of Segment B is preferably less than 2 from the viewpoint of characteristics required for materials for large-diameter gears.
The number average molecular weight of the Segment B can be determined by an osmotic pressure method, a terminal quantitative determination method or by GPC. For example, the number average molecular weight can be determined with a GPC (model 150C unit made by Waters, Co.) at 140xc2x0 C., using 1,2,4-trichlorobenzene as a carrier and polystyrene as a standard sample.
Process for Producing ABA Type Block Copolymer
Description will be made below of a process for polymerizing the present ABA type block copolymer, using Segment B.
The present ABA type block copolymer can be obtained by copolymerizing trioxane and cyclic formal (and/or cyclic ether) in the presence of Segment B as a chain-transfer agent and further by subjecting the resulting block copolymer to a terminal stabilization treatment. During the polymerization of the block copolymer, a molecular weight-controlling agent such as water, methanol, methylal, etc. may be used besides the aforementioned monomer components.
Polymerization can be carried out under conditions as disclosed in JP-A-9-221579 and U.S. Pat. No. 5,837,781 except for the presence of the present Segment B as a chain-transfer agent.
Polymerization catalyst for copolymerizing trioxane and cyclic formal (and/or cyclic ether) is preferably a cationic active catalyst such as Lewis acids, protonic acids and their esters or anhydrides or the like. Lewis acids include, for example, halides of boric acid, tin, titanium, phosphorus, arsenic and antimony, typically, boron trifluoride, tin tetrachloride, titanium tetrachloride, phosphorus pentafluoride, phosphorus pentachloride, antimony pentafluoride and their complex compounds and salts. Specific examples of protonic acids and their esters or anhydrides include perchloric acid, trifluoromethanesulfonic acid, t-butyl perchlorate, acetyl perchlorate, trimethyloxonium hexafluorophosphate, etc., among which boron trifluoride, boron trifluoride hydrate, and coordination complex compounds of oxygen atom or sulfur atom-containing organic compounds with boron trifluoride are preferable, and preferable examples thereof typically include diethyl ether of boron trifluoride and di-n-butyl ether of boron trifluoride. The polymerization catalyst is used in an amount of 1xc3x9710xe2x88x926 molexe2x80x941xc3x9710xe2x88x923 mole, preferably 1xc3x9710xe2x88x925 molexe2x80x941xc3x9710xe2x88x924 mole on the basis of one mole of trioxane.
Polymerization process is not particularly limited, but a bulk polymerization process is preferable. The bulk polymerization may be carried out batchwise or continuously. The bulk polymerization process is a process for obtaining a solid massive polymer in progress of the polymerization, using monomer components in a molten state.
After the polymerization, the resulting block copolymer is put into an aqueous solution or organic solvent solution containing at least one of catalyst neutralizers/deactivators such as amines, e.g. ammonia, triethylamine, tri-n-butylamine, etc., hydroxides, inorganic acid salts, organic acid salts, etc. of alkali metals or alkaline earth metals, followed by stirring in a slurry state usually for a few minutes to a few hours, thereby deactivating the catalyst remaining in the block copolymer.
A process for deactivating the polymerization catalyst by contacting the block copolymer with vapors of ammonia, triethylamine, etc. or a process for deactivating the catalyst by contacting the block copolymer with at least one of hindered amines, triphenylphosphine, calcium hydroxide, etc. by using a mixer can be also used.
Then, the slurry following the catalyst deactivation is filtered and washed to remove the unreacted monomers, catalyst neutralizer/deactivator, and deactivated salts by catalyst neutralization, followed by drying thereby obtaining a block copolymer.
Description will be made below of a process for terminal stabilization treatment of the block copolymer following the polymerization catalyst deactivation. The polymerized block copolymer has thermally unstable hydroxypolyoxymethylene chains at both ends of the polymer, as represented by the following model structure. In the present invention, it is necessary to remove the thermally unstable hydroxypolyoxymethylene chains (unstable terminal chains) by a process involving heating the block copolymer to its melting point or higher or a process involving further contacting with a basic compound as shown below:
HOxe2x80x94MMEMMEMMxe2x80x94Bxe2x80x94MMEMMEMMxe2x80x94OHxe2x86x92HOxe2x80x94EMMEMMxe2x80x94Bxe2x80x94MMEMMxe2x80x94OH+4HCHO (formaldehyde)
(where the underlined portions mean hydroxypolyoxymethylene chains, M means oxymethylene units, E means oxyalkylene units and B means Segment B, and the model structure only shows polymer structures before and after the removal of the hydroxypolyoxymethylene chains, and the distribution state of M and E in the model structure does not always shown the structure of the present ABA type block copolymer).
A preferable process for the terminal stabilization treatment typically comprises contacting the block copolymer melted by a biaxial extruder, etc. with a basic compound such as ammonia, triethylamine, tributylamine, etc. (together with water, if necessary), followed by kneading and removal of vapors of the contacted basic compound and generated formaldehyde.
Segment A
In this manner, the present ABA type block copolymer can be obtained by deactivation of the catalyst and removal of unstable terminal chains. The Segments A present at both ends of the ABA type block copolymer each consists of a polyacetal copolymer residue comprising oxymethylene units [i.e. (CH2O) units] originating from the trioxane subjected to the ring-opening polymerization and oxyalkylene units represented by the foregoing formula (2) originating from the cyclic formal (or cyclic ether) subjected to the ring-opening polymerization. It is preferable that the oxymethylene units and the oxyalkylene units are randomly distributed in the Segment A, i.e. polyacetal copolymer residue.
The present ABA type block copolymer has been subjected to removal of thermally unstable terminal hydroxypolyoxymethylene chains, and thus an oxyalkylene unit represented by the foregoing formula (2) is present at the end of the polyacetal copolymer residue, i.e. the end which is not bonded to the hydroxyalkylene residue (group) present at the end of Segment B. Typically, the terminal group is in a structure represented by the following formula (3): 
[where R2 and j have the same meanings as defined in the formula (2)].
Furthermore, the polyacetal copolymer residue, i.e. Segment A, comprises 95-99.9 mol % of oxymethylene units and 0.1-5 mol % of oxyalkylene units, preferably 98-99.7 mol % of oxymethylene units and 0.3-2 mol % of oxyalkylene units.
Typical examples of the oxyalkylene unit represented by the foregoing formula (2), which originates from cyclic formal (or cyclic ether), includes an ethylene oxide residue, a propylene oxide residue, a 1,3-dioxolane residue, a 1,3,5-trioxepane residue, a diethylene glycol formal residue, a 1,4-butanediol formal residue, a 1,3-dioxane residue, etc., among which preferable oxyalkylene unit is a 1,3-dioxolane residue, a 1,3,5-trioxepane residue and a 1,4-butadiol formal residue, more preferably a 1,3-dioxolane residue, from the viewpoint of block copolymer yield.
It is particularly preferable to use a 1,3-dioxalne residue obtained by polymerizing 1,3-dioxolane having not more than 500 ppm of 2-methyl-1,3-dioxolane and not more than 15 ppm peroxide in terms of hydrogen peroxide as an oxyalkylene unit; and it is further preferable to add 10-500 ppm of one or more of hindered phenols thereto during the polymerization. The content of 2-methyl-1,3-dioxolane can be determined by a hydrogen flame ion detector based on gas chromatography, provided with Gas-chro Pack 55 made by GL Science K.K. The content of peroxide in the 1,3-dioxolane can be determined, typically, by adding 40 ml of isopropyl alcohol, 10 ml of saturated sodium iodide solution (obtained by dissolving NaI in isopropyl alcohol), 2 ml of acetic acid and 25 g of 1,3-dioxolane to a flask, followed by refluxing at 100xc2x0 C. for about 5 minutes, then immediately titrating the mixture with 0.01 N sodium thiosulfate until the color of the mixture is changed from yellow to colorless in the flask to obtain a titration amount (A ml), whereas blank titration is carried out without 1,3-dioxolane in the same manner as above to obtain a blank titration amount (B ml), and calculating the content from the titration amounts thus obtained, using the following calculation equation:
Peroxide content (ppm in terms of hydrogen peroxide)=(Axe2x88x92B)xc3x9717xc3x970.01/(25xc3x971000)xc3x97106
Molecular Weight of ABA Type Block Copolymer
Description will be made below of the molecular weight of ABA type block copolymer.
To satisfy the characteristics required for the present invention, the number average molecular weight of ABA type block copolymer according to the foregoing formula (1) is preferably 10,000-500,000, more preferably 20,000-200,000.
The number average molecular weight of ABA type block copolymer can be calculated by removing Segments B unreacted during the polymerization from the ABA type block copolymer, then reacting the ABA type block copolymer with acetic anhydride at a temperature of not higher than the melting point, thereby acetylating both ends of ABA type block copolymer and quantitatively determining number of acetylated terminals by an infrared absorption spectrum, or the number average molecular weight of ABA type block copolymer can be also determined by GPC.
Determination by GPC can be carried out typically in a GPC unit (model HLC-8120 made by Tosoh Corp.) with 2 columns (HFIP 806, made by Showa Denko K.K., each 30 cm high), hexafluoroisopropanol (hereinafter referred to as HFIP) as a carrier and polymethyl methacrylate (PMMA) made by Polymer Laboratories, as a standard sample, under conditions of temperature: 40xc2x0 C. and flow rate: 0.5 ml/min.
Method for Identifying ABA Type Block Copolymer
Description will be made below of a method for identifying the ABA type block copolymer thus obtained.
First, description will be made of a method for quantitatively determining hydroxyalkylated, hydrogenated polybutadiene that has not undergone chain-transfer.
To quantitatively determine Segment B that has not been chain-transferred, the polymerized block copolymer is first dissolved in HFIP or a good solvent such as dimethyl formamide, etc. (in some cases heating to a temperature of not higher than the melting point of the block copolymer may be carried out for the dissolution purpose), and then water or a poor solvent such as alcohol, etc. is added thereto to reprecipitate only the polyacetal block copolymer, thereby removing Segments B that has not undergone chain-transfer, and the remaining polyacetal block copolymer is quantitatively determined.
To set more precise conditions, it is necessary to prepare Segments B and Segments A independently in advance, then prepare a sample by melting and mixing Segments B and A and confirm whether or not Segments B can be removed entirely from the sample.
Secondly, description will be made of analysis of the monomer composition, which constitutes the polymerized block copolymer.
Block copolymer freed from Segments B that has not undergone chain-transfer in the foregoing manner is hydrolyzed in an aqueous acidic solution such as hydrochloric acid, etc., whereby portions consisting of repeated oxymethylene units are changed to formaldehyde in Segments A, while portions of oxyalkylene units randomly inserted into the polyoxymethylene are changed to alkylene glycol. Segment B is returned to the Segment B before polymerization with Segments A, i.e. hydroxyalkylated, hydrogenated polybutadiene itself.
Formaldehyde and alkylene glycol can be isolated by water extraction and quantitatively determined by gas chromatography. Segment B itself can be quantitatively determined by GPC analysis or gravimetric determination of the residue from the extractive isolation of formaldehyde and alkylene glycol.
Thirdly, description will be made of a method for confirming whether the resulting block copolymer is of ABA type or of AB type.
ABA type block copolymer that is subjected to catalyst deactivation after the polymerization has thermally unstable hydroxypolyoxymethylene chains at both ends of the polymer, as already described above, and the unstable terminal chains can be removed as formaldehyde by heating, etc.
When the block copolymer is of AB type block copolymer, whose only one terminal hydroxyl group is chain-transferred among the hydroxyl groups present at both ends of Segment B, the amount of formaldehyde generated from a block copolymer having an unstable terminal chain at one end by heating, etc. must be a half of that generated from a block copolymer having unstable terminal chains at both ends.
Thus, whether the block copolymer is an AB type block copolymer or an ABA type block copolymer can be confirmed by quantitatively determining the formaldehyde generated by heating the block copolymer.
Typically, a polyacetal copolymer having an equivalent unstable terminal chain to that in case only the hydroxyl group at one end of Segment B has been chain-transferred during the polymerization is prepared by using an equimolar amount of methanol as a chain-transfer agent in phase of the present Segment B. Then, the formaldehyde generated by heating the polyacetal copolymer resulting from polymerization by chain transfer of the methanol is quantitatively determined and compared with the amount of formaldehyde generated by heating a block copolymer resulting from polymerization in the presence of Segment B. When the aldehyde generated by heating the block copolymer resulting from polymerization in the presence of Segment B is in an amount twice as large as that of the aldehyde generated by heating the block copolymer resulting from polymerization by chain transfer of the methanol, it can be confirmed that the block copolymer is an ABA type block copolymer (in view of purity of monomers, polymerization yield, etc., the amount may be twice as large within the so called experimental error accuracy range.
Polyacetal Resin Composition
The present novel ABA type block copolymer itself has a short crystallization time and such characteristics of moldings as high roundness, dimensional stability and durability. Furthermore, the present ABA type block copolymer has distinguished compatibility with other polymer compounds or adhesibility to an inorganic filler, and thus polyacetal alloying, which has been so far difficult to attain, can be realized. A polyacetal resin composition comprising the present ABA type block copolymer has distinguished repeated impact strength, and vibration controllability, etc.
Description will be made below of the present polyacetal resin composition.
The present polyacetal resin composition comprises 100 parts by weight of a polymer compound (I) comprising 20-100% by weight of the above-mentioned ABA type block copolymer and 0-80% by weight of polyacetal copolymer having a number average molecular weight of 10,000-500,000, represented by the following formula (4): 
(where R3 and R4 are independently selected from the group consisting of hydrogen, an alkyl group, a substituted alkyl group, an aryl group and a substituted aryl group; p 95-99.9 mol %; q=0.1-5 mol %; p+q=100 mol % and z is an integer selected from 2 to 6), and 0.1 to 200 parts by weight of at least one of polymer compounds (II) having a number average molecular weight of 500 or more selected from the group consisting of a polyolefin-based polymer compound, a polyurethane-based polymer compound, a polyester-based polymer compound, a polystyrene-based polymer compound, a polyacryl-based polymer compound and a polyamide-based polymer compound.
Formula (4) does not directly show a bonding state of the oxymethylene units represented by (CH2O) and the oxyalkylene units represented by [(CR4R4)zO], and it is preferable that the oxymethylene units represented by (CH2O) and the oxyalkylene units represented by [(CR4R4)zO] are randomly distributed in the polyacetal copolymer represented by formula (4).
Furthermore, in some cases the ABA type block copolymer contains less than 20% by weight of polyacetal copolymer represented by formula (4) (i.e. containing more than 80% by weight of ABA type block copolymer) by the presence of impurities such as water, etc. at the polymerization stage, or by intentional copresence of a chain-transfer agent such as methylal, methanol, etc., but in these cases, the characteristics required for the present invention can be satisfied and thus less than 20% by weight of the polyacetal copolymer, even if contained in the ABA type block copolymer in a such cases, can be handled as an ABA type block copolymer component.
It is preferable from the viewpoint of characteristics required for the present invention that the number average molecular weight of polyacetal copolymer represented by formula (4) is 20,000-200,000.
It is preferable from the viewpoint of characteristic required for the present invention that the polymer compound (I) comprises 30-70% by weight of ABA type block copolymer and 30-70% by weight of polyacetal copolymer represented by formula (4).
Polyolefin-based Polymer Compound
Polyolefine-based polymer compound in the polymer compound (II) includes, for example, homopolymers or copolymers (random, block or graft polymers) of xcex1-olefins such as ethylene, propylene, butene-1, pentene-1,4-methylpentene-1, hexene-1, heptene-1, octene-1, nonene-1, decene-1, undecene-1, dodecene-1, etc., copolymers (random, block or graft copolymers) of the above-mentioned xcex1-olefins and a copolymerizable monomer, etc. The copolymerizable monomer includes, for example, conjugated dienes (butadiene, isoprene, pipelylene, etc.), non-conjugated dienes (1,4-hexadiene, dicyclopentadiene, 5-ethylidene-2-norbornene, 2,5-norbonadiene, etc.), (meth)acrylic acid or its derivatives such as esters, etc. (methyl methacrylate, etc.), (meth)acrylonitrile, aromatic vinyl monomers (styrene, xcex1-methylstyrene, vinyltoluene, p-t-butylstyrene, etc.), vinyl ethers (vinyl methyl ether, etc.) and vinyl esters (vinyl acetate, etc.).
Modified polyolefine-based polymer compounds obtained by graft polymerizing 100 parts by weight of the polyolefin-based polymer compound with 0.01 to 10 parts by weight of unsaturated carboxylic acid (acrylic acid, methacrylic acid, maleic acid, nadic acid, etc.) or its acid anhydride can meet the object of the present invention.
Polyurethane-based Polymer Compound
Polyurethane-based polymer compound is a polymer compound having urethane bonds on the main chain and includes thermoplastic polyurethane, etc. formed by reaction of, for example, a polyisocyanate component (e.g. such polyisocyanate components as aliphatic, alicyclic, and aromatic polyisocyanates, etc.) with a polyol component (e.g. low molecular weight polyol components such as aliphatic, alicyclic and aromatic polyols, etc. or polyetherdiol, polyesterdiol, polycarbonatediol, etc.). In the preparation of polyurethane, a chain propagator (e.g. diol, diamine, etc.) may be used. Furthermore, the present polyurethane-based polymer compound also includes a polyurethane elastomer. The polyurethane-based polymer compound may be not only in a chain structure, but also in a branched chain structure, or may be cross-linked, so far as the thermoplastic property can be maintained. Among these polyurethane-based polymer compounds, polyurethane and polyurethane elastomer, etc. formed by reaction of a diisocyanate component with a diol component are preferable.
Diisocyanate component includes, for example, aliphatic diisocyanates (1,6-hexamethylene diisocyanate, etc.), alicyclic diisocyanates (isophorone diisocyanate, etc.), aromatic diisocyanates (2,4-toluene diisocyanate, 2,6-toluene diisocyanate, 4,4xe2x80x2-diphenylmethane diisocyanate, etc.) and so on. Diol component includes, for example, C2-C10 alkylene diols, polyoxyalkylene glycols [e.g. poly(oxyethylene) glycol, poly(oxypropylene) glycol, poly(oxytetramethylene) glycol or glycols of these copolymers (e.g. polyethylene oxidepolypropylene oxide copolymer, etc.), and so on], polyester diol, etc.
Polyester-based Polymer Compound
Polyester-based polymer compound is a copolymer compound having an ester bond on the main chain and includes, for example, polyalkylene terephthalate (e.g. poly C2-C4 alkylene terephthates such as polyethylene terephthalate, polybutylene terephthate, etc.), polyalkylene naphthalate (e.g. poly C2-C4 alkylene naphthalate such as polyethylene naphthalate, polybutylene naphthalate, etc.), copolyesters containing repeated main units of alkylene terephthalate and/or alkylene naphthalate and also containing copolymer components comprising an acid component resulting from replacement of portions of terephthalic acid and/or naphthalenedicarboxylic acid with other dicarboxylic acid, a diol component resulting from replacement of portions of alkylene glycol with other diol, etc. (The copolyester will be hereinafter referred to merely as xe2x80x9cpolyester-based copolymerxe2x80x9d), aromatic polyesters (e.g. polyarylate, etc. formed by esterification of an aromatic diol such as bisphenol A, etc. and an aromatic dicarboxylic acid such as terephthalic acid, isophthalic acid, etc.), and so on. The present polyester-based polymer compound also includes polyester elastomers and liquid crystal polyesters.
Polyester-based copolymer can be obtained by polycondensation of an acid component comprising 99-50 mol % of terephthalic acid and/or naphthalenedicarboxylic acid and 1-50 mol % of other dicarboxylic acid than the terephthalic acid and/or naphthalenedicarboxylic acid (e.g. aliphatic dicarboxylic acid, alicyclic dicarboxylic acid and aromatic dicarboxylic acid) and a diol component [e.g. C2-C12 alkylene diols (ethylene glycol, trimethyl glycol, propylene glycol, etc.), polyoxyalkylene glycols (di(oxyethylene) glycol, di(oxypropylene) glycol, tri(oxyethylene) glycol, etc.), alicyclic glycols (1,1-cyclohexane dimethylol), 1,4-cyclohexane dimethylol, hydrogenated bisphenol A, etc.), aromatic diols (2,2-bis-(4-xcex2-hydroxyethoxyphenyl) propane, 2,2-bis(4-xcex2-hydroxypropoxyphenyl) propane, etc.) and so on].
Polyester elastomer includes polyester block copolymers, for example, block copolymers comprising a hard segment consisting of polyester units including low molecular weight diols and a soft segment consisting of (poly)ester units including polyether diols or aliphatic polyester diols. Preferable polyester elastomers are polyester elastomers comprising polyethylene terephthalate, polybutylene terephthalate, polybutene terephthalate or polyethylene naphthalate units as a hard segment and esters of polyoxyethylene glycol or polyoxytetramethylene glycol having a molecular weight of about 200 to about 6,000 and terephthalic acid and/or isophthalic acid as a soft segment.
Polystyrene-based Polymer Compound
Polystyrene-based polymer compound is a polymer compound obtained from one or more of aromatic vinyl monomers such as styrene, xcex1-methylstyrene, 2,4-dimethylstyrene, p-methylstyrene, t-butylstyrene, chloromethylstyrene, ethylstyrene, etc. It is particularly preferable to use styrene as a monomer component. Furthermore, the polystyrene-based polymer compound may be copolymers of a component copolymerizable with the above-mentioned aromatic vinyl monomers. Copolymerizable component includes, for example, elastomers, etc. besides copolymerizable unsaturated monomers. Copolymerizable unsaturated monomers include, for example, (meth)acrylonitrile, (meth)acrylic acid ester, maleimide-based monomers, dienes (e.g. butadiene, isoprene, etc.), olefins (e.g. ethylene, propylene, butene, etc.), and so on. Elastomers include, for example, polybutadiene, polyisoprene, ethylene-propylene rubber, acrylic rubber, halogenopolyolefins such as chloropolystylene, etc., and so on, and may be hydrogenation products thereof. One or more each of the copolymerizable unsaturated monomers and elastomers can be used. Above all, it is preferable to use polystyrene-based elastomers consisting of a block (a) comprising an aromatic vinyl monomer and a block (b) comprising isoprene or isoprene-butadiene and having a vinyl bond content (which means the content of 3,4-bonds and 1,2-bonds in case of isoprene and the content of 1,2-bonds in case of butadiene) of 20 mol % or more, preferably 40 mol % or more (where number average molecular weight of block (a) is preferably 2,500 or more). Furthermore, it is more preferable that the block (a) comprising aromatic vinyl monomers consists of two or more of aromatic vinyl monomer components (e.g. an aba type triblock copolymer consisting of different aromatic vinyl monomer components).
Polyacryl-based Polymer Compound
Polyacryl-based polymer compound is a polymer compound comprising (meth)acrylic acid ester as repeated units. The present polyacryl-based polymer compound includes polymers obtained by copolymerization with a monomer such as vinyl compounds, diene compounds, etc., for example, acrylic acid ester, methacrylic acid ester, acrylonitrile, butadiene, ethylene chloride, styrene, etc, as long as the properties of the polymer compound are deteriorated.
Polyamide-based Polymer Compound
Polyamide-based polymer compound includes, for example, polymer compounds synthesized from a diamine component such as 2,5-dimethylhexamethylenediamine, 2,2,4-trimethylhexamethylenediamine, 3-aminomethyl-3,5,5-trimethylcyclohexylamine, etc. and a dibasic acid such as phthalic acid, isophthalic acid, hexahydrophthalic acid, hexahydrophthalic acid, diphenic acid, naphthalenedicarboxylic acid, etc. Furthermore, block copolymers such as poly 2,5-dimethylhexamethylene isophthamide-polyethylene glycol block copolymer, poly 2,5-dimethylhexamethylene isophthamide-polytetramethylene glycol block copolymer, 2,2,4-trimethylhexamethylene naphthalenedicarbamide-polytetramethylene glycol block copolymer, etc. can be used as the present polyamide-based polymer compound.
Above all, a polyacetal resin composition more suitable for the characteristics required for the present invention can be obtained by using 0.1 to 6 parts by weight of a liquid ethylene-xcex1-olefin random copolymer (ethylene unit: 10-70 mol % and xcex1-olefin unit: 30-90 mol %) having a number average molecular weight of 500-10,000 as polymer compound (II). In the moldings resulting from the above-mentioned composition, no peeling phenomena are observed at all on the molding surfaces and the wear resistance of the moldings can be much more improved.
A polyacetal resin composition, which can produce moldings free from peeling thereon and distinguished in repeated impact strength, while satisfying the characteristics required for the present invention can be obtained by using 5 to 200 parts by weight, preferably 10 to 150 parts by weight, of an xcex1-olefin copolymer obtained by modifying an xcex1-olefin-based polymer compound with an unsaturated carboxylic acid (acrylic acid, methacrylic acid, maleic acid, nadicacid, etc.) or its acid anhydride, more preferably an xcex1-olefin copolymer obtained by graft copolymerizing an xcex1-olefin-based polymer compound (copolymer of ethylene and at least one of xcex1-olefins having 3-20 carbon atoms) with 0.01 to 10 parts by weight of an unsaturated carboxylic acid (acrylic acid, methacrylic acid, maleic acid, nadic acid, etc.) or its acid anhydride as polymer compound (II). Thus, even in the gear molding, breakage of a gear tooth (gear teeth) due to collision between gears can be prevented, ensuring a longer gear life.
Furthermore, a polyacetal resin composition, which can produce moldings free from peeling thereon and distinguished in vibration controllability (particularly reduction of hammer hitting noise), while satisfying characteristics required for the present invention can be obtained by using 1 to 100 parts by weight, preferably 5 to 80 parts by weight, of a polystyrene-based polymer compound consisting of a block (a) comprising styrene monomer and a block (b) comprising isoprene or isoprene-butadiene and having a vinyl bond content (which means the content of 3,4-bonds and 1,2-bonds in case of isoprene and the content of 1,2-bonds in case of butadiene) of 20 mol % or more, preferably 40 mol % or more as polymer compound (II). Such a polyacetal resin composition has an expected use in noiseless gears.
The present ABA type block copolymer has a distinguished adhesibility to inorganic fillers such as a glass fiber and the like, and thus is free from disadvantages of inorganic filler fall-off and the like. That is, a polyacetal resin composition comprising 100 parts by weight of the above-mentioned polymer compound (I) and 1 to 100 parts by weight of an inorganic filler provides a gear material capable of improving the mechanical strength and ensuring a high load use as gears, while satisfying the characteristics required for the present invention. Gear materials obtained from such a polyacetal resin composition have an expected use as a material for gears meshing with metallic gears.
One or more of inorganic fillers can be used, and the inorganic fillers include, for example, glass fibers (average fiber diameter: 2-30 xcexcm; 3-10 mm-long chop strands, 30-1,000 xcexcm-long middle fibers and roving type can be particularly used), carbon fibers (average fiber diameter: 2-20 xcexcm; 3-10 mm-long chop strands, 30-1,000 xcexcm-long middle fibers and roving type can be particularly used), glass beads (average particle size: 5-500 xcexcm), talc (average particle size: 5-500 xcexcm), wollastonite (granular or acicular type having a volume average particle size of 0.5-50 xcexcm, or both types can be used together), hydrotalcite, etc. The surface of the inorganic filler may be treated with a well known sizing agent (e.g. urethane sizing agent, olefin sizing agent, epoxy sizing agent, etc.) or a surface-treating agent (e.g. silane type, titanate type, aluminum type, zirconium type, etc.).
Furthermore, a polyacetal resin composition comprising 100 parts by weight of the above-mentioned polymer compound (I), 1 to 100 parts by weight of the above-mentioned inorganic filler and 1 to 20 parts by weight of the above-mentioned polymer compound (II), preferably a polyolefin-based polymer compound, can also meet the characteristics required for the present invention.
Description will be made below of additives, which can be further add to the present polyacetal resin composition.
A polyacetal resin composition suitable for the characteristics required for the present invention can be also obtained by adding to 100 parts by weight of the above-mentioned polymer compound (I) 0.01 to 0.2 parts by weight (sum total) of at least two difatty acid calciums (12-22 carbon atoms) and/or 0.01 to 0.9 parts by weight (sum total) of at least two difatty acid esters (12-22 carbon atoms) comprising fatty acids and ethylene glycol.
The present ABA type block copolymer or polyacetal resin composition can be admixed with other additives than the above-mentioned, when required, for example, hindered phenol-based antioxidants, hindered amine-based light stabilizers, benzotriazole-based ultraviolet ray absorbers, formaldehyde scavengers such as polyamide, melamine, melamine derivatives, poly-p-alanine copolymers, polyacrylamide, etc., pigments such as titanium oxide, carbon block, quinacridene, iron oxide, Titan Yellow, phthalocyanin, aluminum powder, etc., crystal nucleating agents such as boron nitride, etc., solid lubricants such as graphite, molybdenum disulfide, graft polyethylene, PTFE, etc., mold release agents such as ethylene bis-fatty acid amide, etc., antistatic agents such as polyethylene glycol, electroconducrtive carbon black, etc., and so on. It is particularly preferable to add to 100 parts by weight of the block copolymer or the composition 0.1 to 1.0 part by weight of triethylene glycol-bis[3-(3-t-butyl-5-methyl-4-hydroxyphenyl)propionate] as an antioxidant.
Moldings
Description will be made below of moldings prepared from the present ABA type block copolymer or polyacetal resin composition.
The present moldings can be obtained by such molding processes as an injection molding process, a hot runner injection molding process, an outsert molding process, an insert molding process, a blow injection molding process, a high frequency mold heating injection molding process, a compression molding process, inflation molding process, a blow molding process, an extrusion molding process, or a cutting work of the extrusion molding products, etc. From the viewpoint of satisfying the characteristics required for the present invention, moldings obtained by an injection molding process are preferable.
The present moldings are preferably large-diameter gears having a pitch circle diameter of 60 mm or more, more preferably large-diameter gears having a pitch circle diameter of 100 mm or more, obtained by molding the present ABA type block copolymer or polyacetal resin composition.
Particularly preferable moldings are large-diameter gears having a pitch circle diameter of 60 mm or more, or 100 mm or more, for printers or copiers, obtained by injection molding.
The present moldings can be subjected, if required, to decoration such as laser marking, hot stamping, coating, printing, plating, etc. or posttreaments such as welding, bonding, annealing etc.
The present ABA type block copolymer or polyacetal resin composition can be used not only as materials for large-diameter gears, but also as materials for sliding parts to which polyacetal resins are usually used, for example, materials for various sliding parts used in OA machinery, typically printers and copiers; video machinery, typically VTR and video movie; music, image or information machinery, typically, cassette players, LD, MD, CD (including CD-ROM, CD-R and CD-RW), DVD (including DVD-ROM, DVD-R, DVD-RAM and DVD-Audio), navigation systems and mobile personal computers; communications equipments, typically portable phones and facsimile machines; automobile interior and exterior structural parts; industrial gadgets, typically, disposable cameras, toys, fasteners, conveyors, chains, bucles, office utensils and housing equipment, etc.
Typical part names are gears other than large-diameter ones, cams, gear cams, sliders, levers, key stems, key tops, ratchets, rollers, arms, steering wheels, buttons, fly wheels, clutches, joints, shafts, shaft bearings, guide roller, side plates, resin parts of outchassis, chassias, tray members, inner handle bars, outer handle bars, switches, through-anchors, tongues, and dials, etc.